Introduction to Computers
All computer systems can always be partitioned into three basic units: an Input Unit, an Output Unit, and a Processing Unit. The physical components of the system are called hardware, while the programs that execute on this system are called software. The printers and monitors are examples of hardware that are instances of output devices. Examples of input devices are mice, keyboards, and joy-sticks. The Central Processing Unit(CPU) and Memory are elements of the Processing Unit.
Input Unit -------> Processing Unit ---------> Output Unit
The main software that is executed on hardware is the operating system. The operating system is the software that controls the hardware components to work together as a whole. DOS, UNIX, VMS, Windows NT and Windows 95 are all different operating systems. An operating system can also be broken into constituent components called the kernel and the shell. The kernel of an operating system is that component which truly controls the hardware and other resources. The shell, or the command interpreter, is the component of the operating system that is used for communication between the kernel and users. The Microsoft Windows 95 Interface that you see on most microcomputers are implemented by the Shell portion of the Windows 95 operating system. The command line prompt of UNIX is also from the shell portion of the UNIX operating system.